Kalergis enlisted in the U.S. Army in February 1941, prior to
the start of World War II. He was commissioned as a lieutenant
after attending the Field Artillery Officer Candidate School at Fort Sill, Oklahoma in
1942.[1] He
served as an artillery officer with the 882nd Field Artillery
Battalion. By November 1943, he was a captain and battalion
adjutant and promoted to major shortly after the unit arrived in
France in February 1945.[2][3] He was
awarded the Bronze Star while with the 882nd which generally
supported the 70th Infantry Division's 274th Infantry Regiment
during the Rhineland and Central Europe campaigns.[4][5]

From 1949 to 1952, Kalergis, as a major, was assistant professor
of military science and tactics at Saint Bonaventure College, a
Franciscan school in St. Bonaventure, New
York.[6] As a
lieutenant colonel in 1954, Kalergis commanded the 36th Field
Artillery Group's 597th Armored Field Artillery Battalion in Hanau,
Germany.

Vietnam and army
reorganization

In the in 1960s, Kalergis served tours in South Korea and as
commander of 2nd Armored Division
(United States) at Fort
Hood, Texas. During the Vietnam War from 1967 to 1968, he
commanded the artillery for the corps-level organization I Field Force,
Vietnam (United States). The next year, he served as First
Field Force's chief of staff.[2]
In Vietnam, he was recognized in efforts to quantify and reduce
"harassment and interdiction fire", artillery fire intended to
reduce enemy morale and movement. Yet in practice, it was rarely
observed or checked for results and generally proved useless in
countering enemy activities in a war without fronts. Kalergis
developed systems to quantify and significantly reduce its use due
to ineffectiveness, collateral damage to civilians and its high
cost.[7]

In early 1972, Kalergis was recognized for his organizational
abilities and tasked with drawing up the 1973 reorganization of the
U.S. Army, the most extensive reorganization of the Army in the
continental United States since 1942.[8]
Operation STEADFAST resulted in the establishment of U.S. Army Forces Command (FORSCOM) and U.S. Army Training and Doctrine Command
(TRADOC).[9] It was
followed by subsequent reorganizations in Army Staff Headquarters
and of units in the field. The effort to accomplish internal
reorganization was initiated with the Army, forestalling efforts by
the executive or legislative branch in the post-Vietnam era.[10]
Kalergis then served as assistant vice chief for Army Chief of
Staff.

Retirement

In retirement in 1976, Kalerigis chaired a task force that
drafted an action plan Tank Weapon System Management. A Program
for Maximum Effectiveness to improve armored forces
management.[12] His
retirement activities also included serving as a Pentagon
consultant, and from 1979 to 1982 as chairman of Vinnell
Corporation which trained the Saudi National Guard.[2]